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Transistor too hot in VCA?
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Zoomby



Joined: Aug 28, 2006
Posts: 18
Location: Germany

PostPosted: Thu Dec 07, 2006 1:28 pm    Post subject: Transistor too hot in VCA? Reply with quote  Mark this post and the followings unread

Hi,

I build this VCA: http://www.uni-bonn.de/~uzs159/
Unfortunately T4 died dramatically. (current was around 1.5mA and VCE of T4 is always around 15V is it?). I used a BC546. What's wrong? Do I have to cool it? I looked at the datasheet and thought it is OK.

Bye,
Chris
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Blue Hell
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Joined: Apr 03, 2004
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PostPosted: Thu Dec 07, 2006 2:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

VCA2 I guess ?

If your assumption about (or the measurement of) the current is right (and such seems plausible to me) the transistor's internals should be about 6 degrees (Celcius or Kelvin) warmer than it's environment (without cooling used), which is not a problem at all. (assumming a plasic sot54 like packaging having a thermal resistance of 250 K/W).

You didn't accidentily get the collector and emitter exchanged ? (which can happen easily as they come in different packaging types, sometimes with C and E exchanged).

Otherwise something else in the circuit must be wrong causing more current to flow somehow.

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Zoomby



Joined: Aug 28, 2006
Posts: 18
Location: Germany

PostPosted: Thu Dec 07, 2006 4:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi, thanks for the reply!

After another Transistor Barbecue, I changed the resistor which sets the current for the current source from 10K to 1M. Now it works...
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